1. Field of the Invention
The invention relates to a projection display, more particularly to a twin-lens projection display.
2. Description of the Related Art
Referring to FIG. 1, a conventional single-lens projection display 1 is shown to comprise a light source 11, an integrator 12 disposed in front of the light source 11, a dichroic mirror set 13 disposed in front of the integrator 12, a color synthesizing prism 14 disposed in front of the dichroic mirror set 13, three liquid crystal light valves 16 disposed respectively on the left and right sides and the rear side of the color synthesizing prism 14, and two reflective mirror sets 17 disposed respectively adjacent to the left and right sides of the dichroic mirror set 13 and left and right ones of the light valves 16.
In operation, light from the light source 11 passes through the integrator 12 to result in a forwardly directed light beam which is split into primary color components, such as red, green and blue color components, by the dichroic mirror set 13. Each of the primary color components is modulated by a respective one of the light valves 16. Two of the primary color components reach the respective light valve 16 via a respective one of the reflective mirror sets 17. The modulated color components from the light valves 16 are synthesized by the color synthesizing prism 14 for projection by a projection lens 15 so as to form an image on a display screen (not shown).
The color synthesizing prism 14 of the projection display 1 is generally formed from four right-angle prisms, thereby arising in the following drawbacks:
1. The color synthesizing prism 14 is difficult to manufacture in view of the high precision requirement for the four right-angle prisms. If the color synthesizing prism 14 is not precisely formed, the magnification factors for the primary color components will differ from each other, thereby preventing proper overlaying of the color components when forming an image on the display screen.
2. Existing pixel sizes require the cementing lines of the four right-angle prisms to be no thicker than 5 microns so as not to adversely affect the image on the display screen. In the event of an eventual improvement in the resolution of liquid crystal light valves, the cementing lines will unavoidably result in deterioration of the image quality.
3. The color synthesizing prism has an inherent light leakage drawback, which distorts signals of thin film transistors at the back of a liquid crystal display panel that can prevent accurate image formation by a liquid crystal optical projection system.
Referring to FIG. 2, in a conventional triple-lens projection display 2, primary color components are directed to three liquid crystal light valves 21, 22, 23 for modulation. The modulated color components are received by three projection lenses 24, 25, 26, which cooperate to form an image on a display screen 27. The design of the projection display 2 requires the positions of the light valves 21, 22, 23 to be properly offset from the respective projection lens 24, 25, 26 so that image color components can be appropriately combined to form an image on the display screen 27. This complicates the manufacture of the conventional triple-lens projection display 2.
Therefore, the main object of the present invention is to provide a twin-lens projection display that can be manufactured with relative ease and at a relatively low cost.
According to the present invention, a twin-lens projection display comprises:
a color separating mirror set adapted to separate input light into first, second and third color components;
a dichroic synthesizing prism having a first input side, a second input side, and an output side;
an optical path compensating prism having an input side and an output side;
a first light modulator for modulating the first color component from the color separating mirror set, the first light modulator being disposed adjacent to the first input side of the dichroic synthesizing prism, and providing the modulated first color component thereto, the dichroic synthesizing prism outputting the modulated first color component at the output side thereof;
a second light modulator for modulating the second color component from the color separating mirror set, the second light modulator being disposed adjacent to the second input side of the dichroic synthesizing prism, and providing the modulated second color component thereto, the dichroic synthesizing prism outputting the modulated second color component at the output side thereof;
a third light modulator for modulating the third color component from the color separating mirror set, the third light modulator being disposed adjacent to the input side of the optical path compensating prism, and providing the modulated third color component thereto, the optical path compensating prism outputting the modulated third color component at the output side thereof;
a first projection lens disposed adjacent to the output side of the dichroic synthesizing prism so as to receive the modulated first and second color components therefrom; and
a second projection lens disposed adjacent to the output side of the optical path compensating prism so as to receive the modulated third color component therefrom.